The present invention relates to oxide magnetic materials to be used in fields of high frequency and a method of producing the same, as well as coil components of bulk type using the oxide magnetic material, laminated coil components including internal conductors and a method of producing the same.
As oxide magnetic materials such as coil component to be used in fields of high frequency, Nixe2x80x94Cuxe2x80x94Zn based ferrite is in general employed, and a producing method therefor is ordinarily a powder metallurgy method.
This method weighs oxides such as Fe2O3, NiO, CuO or ZnO to be predetermined percentages, wet- or dry-mixes and grinds, and pre-sinters the mixed and ground powders. Subsequently, the pre-sintered material is roughly ground and further finely ground. In a case of the wet-grind, the drying process is necessary.
The characteristics of ferrite much depend on the composition thereof, and from the viewpoint of production management, a composition of a final product should be deviated as little as possible from a target composition.
It is necessary that a material for a laminated coil be sintered at lower temperatures than a melting point of Ag, and in a final product, such a management of the composition is demanded at a level of 0.1 mol % of Fe2O3, NiO, CuO and ZnO. In particular, as to Fe2O3, coming nearer to a stoichiometric composition of ferrite, its reactivity goes up, but exceeding said level, the reactivity rapidly goes down, and accordingly, the most careful management of the composition is required among main components of ferrite.
Incidentally, for a conventional Nixe2x80x94Cuxe2x80x94Zn ferrite, a stainless steel ball, alumina ball or zirconia ball were used as media beads in its manufacturing process, and materials having passed through mixture, grind, and pre-sintering were subjected to a rough and a fine grind. In the material for bulk typed coil, the pre-sintered material is ordinarily ground such that a specific surface area is 1.0 to 7.0 m2/g, and as the laminated typed material is necessarily sintered at lower temperature than a melting point of Ag, a long time is taken for grind, and the specific surface area is heightened to around 3.0 to 15.0 m2/g, thereby to improve the reactivity of the ground powders at low temperature.
In the stainless steel ball, Fe is a main component, and a part of Fe2O3 being a main component in the composition of Nixe2x80x94Cuxe2x80x94Zn ferrite is increased by a mechanochemical reaction when grind. This increase of Fe2O3 changes the composition of Nixe2x80x94Cuxe2x80x94Zn ferrite, and makes a management of stable composition difficult to an extent that the management is not available by weighed values. A difficulty was involved with the abrasion resistance also in other media beads and a problem was that abrasion powders of these beads might be mixed as impurities.
In the general media beads, an inside toughness, that is, the abrasion resistance is low in comparison with an outside toughness, and a deviation in the composition arises due to difference in a mixing amount during continuing productions, so that a stable composition might not be probably obtained, and the grind efficiency is low. In addition, a grind for a long time invites an increase of the mixing amount and deterioration of characteristics of sintered materials, accordingly. Abrasion powders mixed as impurities worsens the sintering property of Nixe2x80x94Cuxe2x80x94Zn ferrite, and sintering temperature becomes high for obtaining a density and a permeability of sintered body in the vicinity of a theoretical density, resulting in a production cost-up and decrease of stability of products, and the sintering below the Ag melting point is difficult.
Japanese Patent No. 2708160 sets forth that, aiming at decreasing mixture of abrasion powders during grind, balls composed of fully stabilized zirconia (called as xe2x80x9cFSZxe2x80x9d hereafter) of large abrasion resistance or partially stabilized zirconia (called as xe2x80x9cPSZxe2x80x9d hereafter) are used as media beads for grinding Mnxe2x80x94Zn based ferrite.
The method disclosed in Japanese Patent No. 2708160 is to use the zirconia balls of 0.5 to 3.0 mm as the media beads in the fine grind process, thereby preventing inclusion of impurities to the most to be below 0.02 wt % vs. the main components. Further, by this method, if the sintering is carried out at lower temperature by around 100 to 200xc2x0 C. with respect to the conventional pre-sintering temperature of 1200xc2x0 C. or higher, a sintered body of the high density near the theoretical density is obtained, so that the sintering temperature decreases industrially and the production cost can be reduced.
Japanese Patent No. 2599887 shows an example that, for a purpose of offering a magnetic material of high mechanical strength, ZrO2 of 0.01 to 3.0 wt % is mixed for main components of materials of Nixe2x80x94Cuxe2x80x94Zn ferrite, and is sintered for 1.5 hours.
Postexamined Japanese patent publication JP-B-6-80613 discloses an example that, for a purpose of offering a Nixe2x80x94Zn ferrite of a high density, Bi2O3 is added in a range of 4 less than Bi2O3xe2x89xa620 wt % with respect to main components of Nixe2x80x94Zn based ferrite to obtain a magnetic material of a high density.
But the sintering temperature in the range of 1000xc2x0 C. described in Japanese Patent No. 2708160 is high and it is not a temperature enabling to realize reduction of the sintering cost. Additionally, when Ag is used as a conductor, a simultaneous sintering with Ag of the melting point being around 960xc2x0 C. is impossible. Being 1100xc2x0 C. as in JP-A-7-133150, it is still more impossible to simultaneously sinter with Ag.
In the method described in the above mentioned Japanese Patent No. 2708160, the media beads of small diameter are used for controlling inclusion of impurities by abrasion of the media beads to be low, and a pre-sintered material is ground taking a long time, for example, 192 hours (8 days), creating a problem that a ball efficiency (material treating amount/ball weight), that is, the grind efficiency is poor.
In the producing method set forth in the above mentioned JP-B-6-80613, a sintering temperature is not clear. In the only example stating a temperature and containing 10 wt % Bi2O3, when the sintering temperature is 950xc2x0 C., the density is around 4.86, and when ds (density) is 5 or higher, the sintering temperature is 960xc2x0 C. or higher. Thus, the simultaneous sintering with Ag is difficult.
In view of the above mentioned problems involved with the prior arts, it is accordingly an object of the invention to provide oxide magnetic materials enabling to simultaneously sinter with Ag as an internal conductor, holding the sintering property and the permeability, and enabling to shorten the grind time, coil components using such oxide magnetic materials as well as a method of producing said oxide magnetic materials and a method of producing said coil components.
For accomplishing the object, the invention is to offer the oxide magnetic materials of the under mentioned (1) to (9), coil components using these oxide magnetic materials, as well as the method of producing the oxide magnetic materials and the method of producing the coil components.
(1) An oxide magnetic material where Fe2O3, ZnO, NiO and CuO are main components, is characterized in that Y2O3, ZrO2 and Bi2O3 are contained with respect to these main components, such that an amount of Y2O3 is 0.007 to 0.028 wt % for the total amount, an amount of ZrO2 is 0.12 to 0.55 wt % therefor and an amount of Bi2O3 is 0.03 to 10.12 wt % for the same.
(2) A coil component of bulk type is characterized in that a sintered substance of the oxide magnetic material as set forth (1) is used.
(3) A laminated coil component is characterized in that a sintered substance of the oxide magnetic material as set forth in (1) is used, and the sintered substance is formed with an electric conductive layer.
(4) The laminated coil components as set forth in (3), characterized in that the electric conductive layer is Ag or Ag.Pd alloy being a main component.
(5) A method of producing oxide magnetic materials wherein Fe2O3, ZnO, NiO and CuO are main components, is characterized by employing a media agitating mill of wet internal circulation type when grind materials having passed through mixture and grind of raw materials and pre-sintering, using partially stabilized zirconia beads as media beads, and containing Y2O3 whose amount for the total amount is 0.007 to 0.028 wt % and ZrO2 whose amount therefor is 0.12 to 0.55 wt %.
(6) A method of producing oxide magnetic materials for coil components wherein Fe2O3, ZnO, NiO and CuO are main components, is characterized by employing a media agitating mill of wet internal circulation type for grind materials having passed through mixture and grind of raw materials and pre-sintering, using partially stabilized zirconia beads as media beads, and containing Y2O3 whose amount for the total amount is 0.007 to 0.028 wt % and ZrO2 whose amount therefor is 0.12 to 0.55 wt %, separately adding Bi2O3 to be 0.03 to 10.12 wt % for the total amount in the oxide magnetic material, and carrying out dispersion by means of the media agitating mill of wet internal circulation type.
(7) A method of producing oxide magnetic materials or oxide magnetic material for coil components as set forth in (5) or (6) is characterized by specifying agitation speed of the media beads to be 4.0 to 10.0 m/s.
(8) A method of producing laminated coil components is characterized by forming and sintering at 880 to 910xc2x0 C. internal conductors in oxide magnetic materials, in which Fe2O3, ZnO, NiO and CuO are main components, and Y2O3, ZrO2 and Bi2O3 are contained with respect to these main components, where an amount of Y2O3 is 0.007 to 0.028 wt % for the total amount, an amount of ZrO2 is 0.12 to 0.55 wt % therefor and an amount of Bi2O3 is 0.03 to 10.12 wt % for the same.
(9) A method of producing laminated coil components as set forth in (8) is characterized in that the internal conductors are Ag or Ag.Pd alloy being a main component.
The under mentioned effects can be performed thereby.
(1) By using the oxide magnetic material in which Fe2O3, ZnO, NiO and CuO are main components, and Y2O3, ZrO2 and Bi2O3 are contained with respect to these main components, where an amount of Y2O3 is 0.007 to 0.028 wt % for the total amount, an amount of ZrO2 is 0.12 to 0.55 wt % therefor and an amount of Bi2O3 is 0.03 to 10.12 wt % for the same, it is possible to offer the oxide magnetic material, the density of which is 5 or higher, the sintering temperature is at the melting points of Ag or Ag.Pd or lower.
(2) As the coil component of bulk type is composed by using the sintered substance of the oxide magnetic material of the above (1), the bulk typed coil component can be composed of a sintered substance, the sintering temperature of which is at the melting points of Ag or Ag.Pd or lower, and the density is 5 or less.
(3) As the laminated coil component is composed by using the sintered substance of the oxide magnetic material of the above (1), it is possible to offer the laminated coil component of the sintered substance to be sintered the low temperature and the high density.
(4) As the internal conductor has the main component of Ag or Ag.Pd, the internal conductor can be composed of a substance of low resistance, and the laminated coil component of high quality factor or coefficient Q can be offered.
(5) As Fe2O3, ZnO, NiO and CuO are main components, containing Y2O3 whose amount for the total amount is 0.007 to 0.028 wt % and ZrO2 whose amount therefor is 0.12 to 0.55 wt %, it is possible to employ the media agitating mill of the wet internal circulation type when grinding the materials having passed through the mixture and the grind of raw materials and pre-sintering, and use partially stabilized zirconia beads as media beads, thereby enabling to solve the difficult problem of managing the composition by much adding Fe as using conventional stainless steel beads.
(6) As the media agitating mill of the wet internal circulation type is employed and the partially stabilized zirconia beads are used as the media beads and Bi2O3 to be 0.03 to 10.12 wt % for the total amount of the main components is added and dispersed when grinding the materials having passed through mixture and grind of the raw materials and the pre-sintering, it is possible to produce the oxide magnetic materials for coil components of the high density in a short time of grind though the sintering is carried out at the low temperature.
(7) In the method of producing the oxide magnetic materials or the oxide magnetic material for coil components in the above (5) or (6), the agitation speed of the media beads is specified to be 4.0 to 10.0 m/s, thereby enabling to shorten the grind time to reduce the production cost and enabling the sinter at the melting point of Ag or lower.
(8) The internal conductor is formed in the oxide magnetic material in which Fe2O3, ZnO, NiO and CuO are main components, and Y2O3, ZrO2 and Bi2O3 are contained with respect to these main components, where an amount of Y2O3 is 0.007 to 0.028 wt % for the total amount, an amount of ZrO2 is 0.12 to 0.55 wt % therefor and an amount of Bi2O3 is 0.03 to 10.12 wt % for the same, and sintered at 880 to 910xc2x0 C., thereby enabling to prevent shortage in sintering or diffusion of electrode materials into the ferrite, and enabling to produce products of less deviation of electric characteristics.
(9) In the method of producing the laminated coil components in (8), the internal conductor is Ag or Ag.Pd alloy being a main component, thereby enabling to produce the laminated coil component of high Q where the internal conductor is composed of a substance having low resistance.